PANCREAS SPECIFIC PROTEIN DISULFIDE-ISOMERASE, PDIP, IS IN TRANSIENT CONTACT WITH SECRETORY PROTEINS DURING LATE STAGES OF TRANSLOCATION

Protein disulfide isomerase (PDI) and an additional lumenal protein of dog pancreas microsomes were previously observed to be in transient c ontact with secretory proteins during late stages of their co- or post translational translocation into these mammalian microsomes, The secon d protein was characterized as a 57 kDa glycoprotein, Here we identifi ed this glycoprotein as the canine equivalent of human PDIp, a protein which was recently described as a new protein disulfide isomerase whi ch is highly expressed in human pancreas, Canine PDIp is also a very a bundant protein, its concentration in pancreatic microsomes approaches the concentration of PDI and of the major microsomal molecular chaper ones. Apparently, PDIp shares with PDI not just the enzymatic but also the polypeptide binding or chaperoning activity, Furthermore, we sugg est that PDIp, too, can be involved in completion of cotranslational a s well as posttranslational translocation of proteins into mammalian m icrosomes. (C) 1997 Federation of European Biochemical Societies.